1. Field of the Invention
The present invention is directed to system and method for generating plasma discharge and, in particular, to a segmented electrode capillary discharge, non-thermal plasma process and apparatus.
2. Description of Related Art
A xe2x80x9cplasmaxe2x80x9d is a partially ionized gas composed of ions, electrons, and neutral species. This state of matter is produced by relatively high temperatures or relatively strong electric fields either constant (DC) or time varying (e.g., RF or microwave) electromagnetic fields. Discharged plasma is produced when free electrons are energized by electric fields in a background of neutral atoms/molecules. These electrons cause electron atom/molecule collisions which transfer energy to the atoms/molecules and form a variety of species which may include photons, metastables, atomic excited states, free radicals, molecular fragments, monomers, electrons, and ions. The neutral gas becomes partially or fully ionized and is able to conduct currents. The plasma species are chemically active and/or can physically modify the surface of materials and may therefore serve to form new chemical compounds and/or modify existing compounds. Discharge plasmas can also produce useful amounts of optical radiation to be used for lighting. Many other uses for plasma discharge are available.
U.S. Pat. Nos. 5,872,426; 6,005,349; and 6,147,452, each of which are herein incorporated by reference, describe a glow plasma discharge device for stabilizing glow plasma discharges by suppressing the transition from glow-to-arc. A dielectric plate having an upper surface and a lower surface and a plurality of holes extending therethrough is positioned over a cathode plate and held in place by a collar. Each hole in the dielectric acts as a separate active current limiting micro-channel that prevents the overall current density from increasing above the threshold for the glow-to-arc transition. This conventional use of a cathode plate is not efficient in that it requires the input of a relatively high amount of energy. In addition, the reactor requires a carrier gas such as Helium or Argon to remain stable at atmospheric pressure.
It is therefore desirable to develop a device that solves the aforementioned problem.
The present invention consists of a system for generating non-thermal plasma reactor system to facilitate chemical reactions. Chemical reactions are promoted by making use of the non-thermal plasma generated in a segmented electrode capillary discharge non-thermal plasma reactor, which can operate under various pressure and temperature regimes including ambient pressure and temperature. The device uses a relatively large volume, high density, non-thermal plasma to promote chemical reaction upon whatever fluid is passed through the plasma (either passed through the capillary or passed transverse through the resulting plasma jet from the capillary. Examples of the chemistry, which could be performed using this method, include the destruction of pollutants in a fluid stream, the generation of ozone, the pretreatment of air for modifying or improving combustion, the destruction of various organic compounds, or as a source of light. Additionally, chemistry can be performed on the surface of dielectric or conductive materials by the dissociation and oxidation of their molecules. In the case of pure hydrocarbons complete molecular conversion will result in the formation of carbon dioxide and water, which can be released directly to the atmosphere.
The reactor in accordance with the present invention is designed so that the gaseous stream containing chemical agents such as pollutants are exposed to the relatively high density plasma region where various processes such as oxidation, reduction, ion induced decomposition, or electron induced decomposition efficiently allow for chemical reactions to take place. The ability to vary the plasma characteristics allows for tailored chemical reactions to take place by using conditions that effectively initiates or promotes the desired chemical reaction and not heat up the bulk gases.
In a preferred embodiment of the present invention the plasma reactor includes a first dielectric having at least one capillary defined therethrough, and a segmented electrode including a plurality of electrode segments, each electrode segment is disposed proximate an associated capillary. Each electrode segment may be formed in different shapes, for example, a pin, stud, washer, ring, or disk. The electrode segment may be hollow, solid, or made from a porous material. The reactor may include a second electrode and dielectric with the first and second dielectrics separated by a predetermined distance to form a channel therebetween into which the plasma exiting from the capillaries in the first dielectric is discharged. The fluid to be treated is passed through the channel and exposed to the plasma discharge. If the electrode segment is hollow or made of a porous material, then the fluid to be treated may be fed into the capillaries in the first dielectric and exposed therein to the maximum plasma density. The fluid to be treated may be exposed to the plasma discharge both in the capillaries as well as in the channel between the two dielectrics. The plasma reactor is more energy efficient than conventional devices and does not require a carrier gas to remain stable at atmospheric pressure. The plasma reactor has a wide range of application, such as the destruction of pollutants in a fluid, the generation of ozone, the pretreatment of air for modifying or improving combustion, and the destruction of various organic compounds, and surface cleaning of objects.
The present invention is directed to a plasma reactor including a first dielectric having at least one capillary defined therethrough, and a segmented electrode including a plurality of electrode segments, each electrode segment disposed proximate an associated capillary.
In addition, the present invention also provides a method of treating a fluid in a plasma reactor as described above. Initially, a fluid to be treated is passed through one or more electrode segments and associated capillaries. The fluid is able to pass through the electrode segment if the segment is hollow or made of a porous material. The fluid to be treated while being passed through the capillary is exposed to the plasma discharge prior to exiting from the capillary. In addition, or instead of, passing the fluid to be treated through the electrode segment, the fluid to be treated may be passed through a channel defined between the first dielectric and a second dielectric. In the channel, the fluid to be treated is exposed to plasma discharged from the capillary. Accordingly, the fluid to be treated may be passed and exposed to the maximum plasma density in the capillaries defined in the first dielectric as well as in the plasma region (channel) between the two dielectrics.